15-Year vs. 30-Year Mortgage: The Real Math
· 7 min read
Choosing between a 15-year and a 30-year mortgage is a trade-off between two very different currencies: monthly cash flow today versus total wealth tomorrow. The 30-year wins the first. The 15-year overwhelmingly wins the second. Here are the actual numbers so you can see what each choice really costs.
Side by Side: $350,000 Loan
Let's compare the two most common setups using realistic 2026 rates: 6.5% for a 30-year fixed and 5.875% for a 15-year fixed (15-year rates typically run 0.5–0.75 points lower).
| Item | 30-Year @ 6.5% | 15-Year @ 5.875% |
|---|---|---|
| Monthly principal & interest | $2,212.24 | $2,929.91 |
| Total paid over the loan | $796,406 | $527,384 |
| Total interest cost | $446,406 | $177,384 |
| Interest as % of loan | 128% | 51% |
| Paid off in | 30 years | 15 years |
The differences are stark:
- The 15-year payment is $717.67 higher per month (+32%).
- The 15-year saves $269,022 in total interest — more than three-quarters of the original loan amount.
- You own the home outright 15 years sooner.
Why the Gap Is So Large
Two forces compound in the 15-year's favor:
- Time. Interest accrues every month on the remaining balance. Halving the time roughly halves the period during which a large balance is generating charges.
- Faster principal reduction. Every extra dollar of monthly payment goes straight to principal, which shrinks the base on which future interest is calculated. The effect snowballs.
Add the lower rate lenders offer on shorter terms and the result is the $269,000 gap above. On smaller loans the absolute number shrinks, but the pattern holds: a 15-year term typically cuts lifetime interest by more than half.
What the Higher Payment Requires
A $2,929.91 payment needs to fit your debt-to-income ratios. Using the 28% front-end rule:
$2,929.91 ÷ 0.28 ≈ $10,464 gross monthly income (~$125,600/year), assuming modest taxes and insurance.
That does not mean a 30-year borrower earning less cannot benefit — it means the 15-year product demands a stronger income or a smaller loan. Many buyers instead take the 30-year and simulate the 15-year with voluntary extra payments, keeping the mandatory payment low.
The Hybrid Strategy: 30-Year Loan, 15-Year Discipline
Taking the 30-year loan and paying an extra $717.67 every month produces almost exactly the 15-year outcome — our calculator shows a $350,000 loan at 6.5% retired in about 16 years when you add $720/month. You give up maybe a few thousand dollars versus the true 15-year (because of the higher rate) but gain something valuable: the right to stop.
If you lose your job or face a medical bill, the required payment is still only $2,212.24. With a real 15-year mortgage, there is no pause button.
This flexibility has a price discipline problem, though: money not automated tends to get spent. If you know yourself well enough to be honest here, that answers the question too.
Which One Should You Choose?
- Choose the 15-year if: the payment fits comfortably under 28% of your income, you value being debt-free early, retirement is within 15–20 years, and your emergency fund is already solid.
- Choose the 30-year if: you need maximum cash flow for childcare, investments, or an uncertain income; you plan to invest the difference; or buying at all would be impossible with the shorter-term payment.
- Consider the hybrid if: you want 15-year economics but refuse to accept 15-year rigidity.
Run both terms through a full amortization schedule before deciding — seeing the exact month your balance hits zero changes how the decision feels.
Frequently Asked Questions
How much interest do you save with a 15-year mortgage?
On a $350,000 loan, a 30-year fixed at 6.5% costs about $446,400 in total interest, while a 15-year fixed at 5.875% costs about $177,400. That is a saving of roughly $269,000 over the life of the loan — more than the original loan amount itself.
Is it better to get a 15-year mortgage or pay extra on a 30-year?
Paying extra on a 30-year gives you nearly the same savings with more flexibility. If money gets tight, you can drop back to the required payment; with a 15-year loan the higher payment is mandatory. The trade-off is that 15-year loans carry lower rates, so they still win slightly on pure interest math.
What salary do I need for a 15-year mortgage?
A common guideline is that the payment should stay within 28% of gross monthly income. A 15-year payment of about $2,930 per month implies a gross income of roughly $10,500 per month, or about $125,000 per year, depending on taxes, insurance, and other debts.
Can I refinance from a 30-year to a 15-year mortgage later?
Yes, many homeowners do exactly that when their income rises or rates fall. Watch the closing costs (typically 2 to 5 percent of the balance) and compute your break-even point first. If rates dropped since you bought, the refinance can cut both your rate and your remaining term at once.